1. SYS364 Database Design Continued

2. Database Design Definitions Initial ERD’s Normalization of data Final ERD’s Database Management Database Models File Access and Organization

3. Database Management File processing environments where each user/department has its own copy of files (or data in spreadsheets) have three problems Data redundancy Inconsistent data Managers require enterprise-wide information A database is a normalized, single repository optimized for transactions. A data warehouse is optimized for read only data inquiry and may not be normalized. Updated by the transaction database at intervals.

4. Elements of Database Management Systems DBMS is a software system used to create, access and control a database Has five main components Data Definition Language Data Manipulation Language Query language Data dictionary Utility programs

5. Data Definition Language Used to describe the structure of the database Complete database description (fields, records and relationships) is the schema or collection Subschema is a view of the database as seen by a program or a user

6. Data Manipulation Language Provides necessary commands for database operations Select Insert Update Delete

7. Query Language A non-procedural language used to access a database Non-procedural languages allows you to specify a task without specifying how the task will be done QBE (Query By Example) SQL (Structured Query Language)

8. Data Dictionary Serves as a central repository for information about the database Schemas and subschemas are stored in the data dictionary

9. Utility Programs Most DBMS include the necessary support for database security, backup and recovery, audit trails, and data integrity Most DMBS also provide utility programs for creating a database, changing the structure of the database, gathering and reporting patterns of database usage, and detecting and reporting database structure irregularities

10. Characteristics of Database Management Programs independent of Data storage Scalability – accommodates growth Support for client/server Central repository: Economy of scale – one big server Data exists once and is shared (not copied) DB Admin. Enforces standards, balances specific requirements vs. overall performance Controls DB Replication when needed Security

11. Database Models Hierarchical & Network old, e.g. FoxPro, dBase Programs must know relationships Object-oriented good for BLOBs and non-transactional data Relational the current standard, SQL interface ad hoc (to this) interactive processing Embedded in programs ODBC, JDBC

12. File Access and Organization Logical vs. Physical Records Types of files Control files, e.g. next numbers for Customer code, SKU, Invoice No. Master file, e.g. Customer, Inventory Transaction Files, e.g. Invoices (updated, volatile) Audit/Journal Files, who did what and when History Files, e.g. old Invoices (read-only, non-volatile) Work Files, temporary use

13. File Access Sequential Access Method (all records in sequence, usually by primary key) Random Access Method (any one record) Various programming techniques must be used in non-DBMS systems DBMS is all by key, Sequentially or Randomly through program interfaces and/or imbedded SQL

14. File Organization File (non-DBMS) systems: Sequential Organization (sorted records) Direct Organization (relative record number) Indexed Organization (simple key but no relations) DBMS Tables in 3NF with Primary Keys, Views of data across tables by relationships

15. Storage Media HDD – cheap, fast DASD –good, faster RAID1 – mirrored redundancy: fast, good RAID5 – striped redundancy: cheaper, fast Floppy vs. diskette Tape, CD-ROM, removable media  ensure capacity for unattended backup Hierarchical file systems